Soleus muscle

The soleus muscle is a broad, flat muscle located in the posterior compartment of the lower leg, deep to the gastrocnemius. It originates from the posterior aspect of the proximal tibia (including the soleal line), the proximal third of the fibula, and the interosseous membrane. The muscle fibers converge distally to insert via a central tendon that joins the gastrocnemius aponeurosis to form the Achilles tendon, which attaches to the calcaneal tuberosity. The soleus is characterized by a complex architecture with both anterior bipennate and posterior unipennate compartments, and it is innervated by branches of the tibial nerve. Its primary function is plantarflexion of the ankle, contributing significantly to postural stability and locomotion.

Origin: Fibula, medial border of tibia (soleal line)

Insertion: Tendo calcaneus

Artery: Sural arteries

Nerve: Tibial nerve, specifically, nerve roots L5–S2

Action: Plantarflexion

Antagonist: Tibialis anterior muscle

Description: The Soleus is a broad flat muscle situated immediately in front of the Gastrocnemius. It arises by tendinous fibers from the back of the head of the fibula, and from the upper third of the posterior surface of the body of the bone; from the popliteal line, and the middle third of the medial border of the tibia; some fibers also arise from a tendinous arch placed between the tibial and fibular origins of the muscle, in front of which the popliteal vessels and tibial nerve run. The fibers end in an aponeurosis which covers the posterior surface of the muscle, and, gradually becoming thicker and narrower, joins with the tendon of the Gastrocnemius, and forms with it the tendo calcaneus.

Variations.—Accessory head to its lower and inner part usually ending in the tendocalcaneus, or the calcaneus, or the laciniate ligament.